Harper Lee was working as an airline reservations agent in New York City, struggling to write a novel tentatively titled "Atticus," when a close friend gave her enough money to take time off and finish her book. Published in 1960 with an initial print run of just 5,000 copies, "To Kill a Mockingbird" became an instant phenomenon: a critically acclaimed bestseller and Pulitzer Prize winner, followed by a multiple-Oscar-winning 1962 film featuring the iconic performance of Gregory Peck as courageous Southern lawyer Atticus Finch.

Fifty years and more than 30 million copies of the book later, it's hard to find any American who doesn't know the names Scout, Boo Radley and Atticus. Lee's one and only novel has been translated into 40 languages and is the most widely read book in American high schools. The novel and film are so familiar, in fact, that last month, when the U.S. Postal Service issued a commemorative stamp honoring Peck, it featured him as he appeared in that Oscar-winning role.

"I can't name another novel that has these kinds of indelible characters, a social statement without being preachy, and good prose," says filmmaker Mary McDonagh Murphy, whose documentary, "Hey, Boo: Harper Lee and To Kill a Mockingbird," opens Friday. "It's a book that many people can relate to in many different ways."

Lee "creates a believable fictional landscape that you can go into," adds Charles J. Shields, author of "Mockingbird: A Portrait of Harper Lee." "The book asks one of the most important questions facing humans — how to get along with people different from us. It was couched in racial terms back then, but today I believe it's about people who don't believe the same as you — different religious beliefs, gays, straights. There are a lot of things that can be discussed."

And that discussion has meaning no matter the age of the reader. In fact, Murphy, an independent writer-producer who had an Emmy Award-winning career at CBS News, decided to pursue a film about Lee and her book after rereading it as an adult.

That experience, she says, "made a greater impression on me than my adolescent reading. I went exploring to see what I could find out about the novel, the novelist and its impact. And I explored the context in which it was published. The book spoke to me more about conscience and integrity this time than it had before. I began to see the story [for the film] was the novel, the novel was the phenomenon. The novel could be the story, not the novelist."

Besides, she adds, it's not as if Lee — who at 85 hasn't given an interview in decades — "was going to invite me to tea."

Lee was a small-town Alabama native, writing about a corner of the state she was familiar with. She intended her work "to be kind of a regionalist piece," Shields says. "She said she wanted to be the Jane Austen of the South."

In that respect she was successful, painting a portrait of a time and place — a small town in the 1930s, a young girl's coming of age and a fearless lawyer who defends a black man in a racially charged trial — that fits snugly into a classic Southern literary tradition.

The book focuses "on the racial tension, and there's a strong sense of place, painting the portrait of [the fictional town] of Maycomb, Ala., on the first page," says Jill McCorkle, a novelist who teaches creative writing at North Carolina State University. "There's also a compassion for outsiders and those who don't fit into the mainstream that you see in the works of writers like Carson McCullers and William Faulkner. And there's a great emphasis on poverty, the way children are viewed in terms of class issues. It's a microcosm of what the great big world looks like."

This worldview is one of several reasons why "To Kill a Mockingbird" has attracted such a huge audience. And Murphy's film, which includes interviews with such fans of the book as Oprah Winfrey, Tom Brokaw, Rosanne Cash, James Patterson and Anna Quindlen, makes the point that Lee's novel is enjoyed by a mixed bag of genders, races and ages. "What I found fascinating about doing what I did," says Murphy, referring to making the documentary and asking people what they responded to in the book, "what really surprised me was every time I went somewhere, every single time I heard something I had never heard before about this novel."

Murphy's film, which runs 82 minutes, takes a nonlinear approach to Lee's story. Beginning in the 1950s, when Lee was writing her book, "Hey, Boo" jumps around to cover various aspects of her story. Titled sections, which include numerous "talking head" interviews, deal specifically with the characters of Scout, Boo and Atticus; others handle what the South that Lee grew up in was like.

In a boon for the film, Murphy obtained interviews with Lee's 99-year-old sister, Alice, as well as her New York friends, Michael and Joy Brown. There is also material involving Lee's friend Truman Capote — who, jealous of her Pulitzer Prize, claimed he had helped write the book — and speculation as to why Lee never wrote another novel (fear of failure after a monster debut is one possibility).

For all its effect, it's not as if "To Kill a Mockingbird" has never courted controversy. The book was published practically at the dawn of the civil rights movement, before such seminal events as the freedom rides, the Birmingham church bombing, the Selma to Montgomery march and the march on Washington. In this respect, an honest book about Southern racism, written by a 34-year-old white female, can be seen as an almost revolutionary act.

"I find a writer like Harper Lee extremely brave," says Jocelyn Chadwick of the National Council of Teachers of English, "because she is a Southern woman. I'm sure people felt, 'How could you betray the South in such a way?'"

"I think [Lee] understood segregation very well from a white liberal point of view, and she's sympathetic to blacks and the problems they face," adds Lisa Dorr, who teaches history at the University of Alabama, which Lee attended for several years. "The book opened the eyes of whites, and made them see how segregation worked."

But the book has also been criticized for the many times the N-word pops up, despite the historical accuracy of the term's usage. And Lee's two prominent black characters — Calpurnia, the Finches' maid, and Tom Robinson, the man unjustly accused of rape — have been condemned from a number of quarters.

"They're sentimentalized," says Shields, who notes that when he gives talks about Lee and the book, "I see very few black faces. Tom Robinson is well-meaning, and Calpurnia is always available. It's very much a white patriarchal view of blacks as children."

Yet interest in the book, and its author, seems never to have waned. "To Kill a Mockingbird" sells about 100,000 copies a year, the film pops up on TV on a regular basis, and it just screened in Los Angeles last weekend as part of Turner Classic Movies' Classic Film Festival (The American Film Institute has also named Peck's portrayal of Finch the greatest movie hero of the 20th century). And even today, there is controversy over a new biography of the author from writer Marja Mills, who says she had the full cooperation of both Alice and Harper Lee, though the latter now denies she participated.

The mystery of Lee and why she never wrote another novel perhaps helps keep the book alive, but there clearly is more to it than that. "At the heart of this novel is a philosophy that speaks to humanity and a kindness and compassion that crosses all the lines," McCorkle says.

Adds Murphy: "I am always impressed by the transforming power of reading, and this is a novel that has made a difference to millions of readers. For all this discussion about social networks, the people who read 'To Kill a Mockingbird' are one of the greatest social networks of all time. In this film, I wanted to address the impact that one book can have."